Testing device for modubated high frequency



July 24, 1934. K. HALLEN TESTING DEVICE FOR MODULATED HIGH FREQUENCY Filed June 16, 1952 METER CZ 6- U U UM Patented July 24, 1934 1,567,306 TESTING DEVICE FOR oDUnATED mum FREQUENCY '.Karl Hallen, Berlin-Tempelhof,.Germanm assignor to. C. Lorenz,Aktiengesellsclialftl Ber-lin Tempelhof, Germany, a company 'i Application June 16,1932;,Serial'No. 611559 v lnGermany July 3; 193b I l 6 Claims. (01. 179-171) The supervision of high frequency transmittersrequir'es measurement of the ratio of k the amplitude" of themodulatingfrequency to the mp1s tude of the'carrier" frequency; Thisratio indiifif'cates theamount or degreeof modulatiomofthe transmitter. It can be seen from this ratio -to what an extentthetransmitteris being utilized.

A well-knownmethod of ascertaining the de'- gree* of -"-rnodulation consistsin" ascertaining the 1111 peakvoltages 'ofthe unmodulatedand the modu-' lated carrier frequencies and there'from to calculate the degreeof modulation. Amplifying volt meters re employedwith this' method, i; e; de-- vices thatonly indicate the correct value if the anode, grid-, and filamentvoltagesare the same as" they were oncalibration.

'A'nother method makes use-of the -Braun tube. The inventiondescribed hereinafter has for its obj eat" to provide an arrangement that{shall=indi-' rcate the degree ofmodulialtiori directly.- This is obtained by means of rectifiers and device adapted to indicate tlie ratio whieh existsbetween direct currents. A crossed ooibmeasuringi iristr-unierit is aaapred ror" this purpose, as willbe'understood from the iollowing description and be particularly pointed oiit in the appended drawing in which Fig. 1- showsthecircuit arrangement of-one' eim' 3g bodirxie'nt of theinventioni Fig; Z-isadiagrarir claims, reference being had tothe'accompariying that mummies part of the operation thereon ammeter, G2 a second rectifier, C a condenser.

These parts are connected in the manner shown The transformer T1 conducts the modulated high frequency to the rectifier G1. This energy is represented in Fig. 2 by the curve m. The device G1 acts to rectify this energy so as to cause a direct current to flow over a, RI, TII, A, TI, G1. This current JG, which is the mean value of the rectified, i. e. demodulated carrier frequency, is in Fig. 2 represented by line p. The modulating frequency, illustrated by curve w, Fig. 2, is owing "150 such rectification superposed on this direct curre'nt or in asense separatedtherefrom: It is conducted by the-transformer" 'III 'to the rectifier G2; 'Ihe-direct currenmmb wliicli=the modulating frequency is =tliu's cohverted flews through-the coil" 1) 'and resistance RIF. Condenser C and re- 6 sistance RH are-:8 dimensionedthat the timecbristant -of the" lowest frequency} ii I ez about: 30 cycles per second} is" so trifling that in may be neglected on measuring this frequency, condenser C hence being always charged to the -peal voltage-so that the durrent flewirig thrbugh resistance RH and" doil U isro ortionate this voltage;

oondens'er- G is' alsdeffective to y -passarmradm frequency current flowing i l the secondary of transformer TIP and to insure that only "the fre-' quency' of the niodlllatiiig our rent will existdn'the current flowing through coil b of the measuring instrument Iiine t in Fig. l 2" indicates tlie rhean value Jih of the rectified modulatedcarrienfiequenoy; The I part uof the curve" shown in Figi 2 represents the demodulated carrier ire'quenc'y; The r'eiiti-- fi'cation oi the part it is illustrated by the upper" halves of this par t and the dotted-line halvestherebetweenl Theexpression upper Halves means those'half-waveswliiehinthe drawingare' above thezero line-- In order-to be able to calibrate the instrument K in degrees of modulation it is necessaryto" provide for a definite mutual; ratio of the re sistance's*RI and RiIlgbecause the ciiiiiitJG th'at is activ'ein -th'e coil a is s?!'nallei th'a'n the mean value Jm therectifiedriiodlilat'ecl carrier ire quency, as will be seen from Fig. 2. This is due to the fact that only this direct current JG is it active in the instrument K. The current JG is to the mean value Jm as is 1r 1; This value is obtained by integrating the sine curve. If, therefore, the ratio of the resistance is such that value JG of the carrier current remains constant or not, whilst in the case of two measurements such constancy is requisite. Any varia- 11d tions of this mean value which may occur on modulation are indicated by the ammeter A of the demodulation circuit or circuit of the rectifier G1, that is the circuit which contains the parts G1, a, RI, and the primary of TII.

If the transformer TI is so connected to the antenna that with non-modulation of the transmitter the deflection of the ammeter A amounts to 100 parts of the scale thereof, then if the carrier amplitude happened to vary on modulation, such variation is by the instrument A indicated in percentage values of the mean of the unmodulated wave.

The modification shown in Fig. 3 difiers from the arrangement disclosed in Fig. 1 by this feature only that a single-way rectifier G3 is utilized instead of the double-way rectifier-Gzrepresent ed in Fig. 1. This is useful, for instance, if the modulating frequency is not purely sinusoidal. For example, the upper amplitudes may occur to be larger than the lower ones. The rectifier G3 also in such event secures a reliable test reading. The upper or lower maximum values of the modulating oscillation may here be measured ,after the polarity of the primary or secondary of the transformer has been reversed.

The crossed-coil measuring instrument K may be replaced by any other device adapted for the purpose.

30, 7 -What is claimed is:

1. In a testing device for modulated high frequency, a rectifier, means for leading to said rectifierrthe modulated high frequency energy to be tested, a second rectifier, means for supplying said 5 second rectifier with the modulating frequency from the output of said first-mentioned rectifier, an instrument adapted to indicate the mutual ratio of two direct currents, and means for conducting the rectified currents fromthe two said rectifiers through this instrument.

2. In a testing device for modulated high fre quency, a rectifier, means for leading to said rectifier the modulated high frequency energy to be tested, a second rectifier, means for supplying said second rectifier with the modulating fre- "quency from the output of said first-mentioned rectifier, a cross-coil instrument for indicating the mutual ratio of two direct currents, and means for conducting the rectified currents from the two said rectifiers through this instrument.

3. In a testing device for modulated high frequency, a rectifier, means for leading to said rectifier, the modulated high frequency energy to be 4. In a testing device for modulated high frequency, a rectifier, means for leading to said rectifier the modulated high frequency energy to be tested, a second rectifier, means for supplying said second rectifier with the modulating frequency from the output of said first-mentioned rectifier, an instrument adapted to indicate the mutual ratio of two direct currents, means for conducting the rectified currents from the two said rectifiers through this instrument, and a capacity connected in parallel with the second said rectifier.

5. In a testing device for modulated high frequency, a rectifier, means for leading to said rectifier, the modulated high frequency energy to be tested, a second rectifier, means for supplying said second rectifier with the modulating frequency from the output of said first-mentioned rectifier, an instrument adapted to indicate the mutual ratio of two direct currents, means for conducting the rectified curents from the two said rectifiers through this instrument, an ammeter, disposed in the circuit of the first said rectifier, for indicating on modulation the percentage difference between the mean value of the carrier amplitudes and the amplitude of the non-modulated frequency. I

6.'In a testing device for modulated high frequency, a rectifier, means for leading to said rectifier the modulated high frequency energy to be tested, a single-way rectifier, means for no supplying said second rectifier with the modulating frequency from the output of said firstmentioned rectifier, an instrument adapted to indicate the mutual ratio of two direct rectified currents, and means for conducting the currents l from the two said rectifiers through this instrument.

KARL HALLEN. 

